42 atheist celebrities, comedians, scientists and writers give their funny and serious tips for enjoying the Christmas season.Last year, Guardian journalist Ariane Sherine launched the Atheist Bus Campaign and ended up raising over 150,000, enough to place the advert 'There's probably no God. Now stop worrying and enjoy your life' on 800 UK buses in January 2009. Now Ariane and dozens of other atheist writers, comedians and scientists are joining together to raise money for a very different cause.The Atheist's Guide to Christmas is a funny, thoughtful handbook all about enjoying Christmas, from 42 of the world's most entertaining atheists. It features everything from an atheist Christmas miracle to a guide to the best Christmas pop hits, and contributors include Richard Dawkins, Charlie Brooker, Derren Brown, Ben Goldacre, Jenny Colgan, David Baddiel, Simon Singh, AC Grayling, Brian Cox and Richard Herring.The full book advance and all royalties will go to the UK HIV charity Terrence H